Drug delivery devices allowing for multiple dosing of a required dosage of a liquid medicament, such as liquid drugs, and further providing administration of the medicament to a patient, are as such well-known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe.
Drug delivery devices of this kind have to meet a number of user specific requirements. For instance in case of those with diabetes, many users will be physically infirm and may also have impaired vision. Therefore, these devices need to be robust in construction, yet easy to use, both in terms of the manipulation of the parts and understanding by a user of its operation. Further, the dose setting must be easy and unambiguous and where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose. In order to meet these requirements, the number of parts and steps required to assemble the device and an overall number of material types the device is made from have to be kept to a minimum.
Typically, the medicament to be administered is provided in a cartridge that has a moveable piston or bung mechanically interacting with a piston rod of a drive mechanism of the drug delivery device. By applying thrust to the piston in a distal direction, a predefined amount of the medicinal fluid is expelled from the cartridge.
In particular for elderly or physically infirm users, the overall handling of the device in a home medication environment should be simple and highly reliable. As for instance illustrated in FIGS. 1 to 3, drug delivery devices and in particular pen-type injectors typically comprise a multi-component housing. Here, a distal end section typically serves as a cartridge holder 12. The cartridge holder 12 comprises a threaded socket 16 at its distal end to receive a needle assembly 18 having a correspondingly threaded needle hub 20 and a double tipped injection needle 22.
The cartridge holder 12 further comprises an insert portion 26 at its proximal end section, by way of which the cartridge holder 12 can be at least partially inserted into a correspondingly shaped distal receptacle of a proximal housing component 14 of the drug delivery device, typically denoted as body 14. The body 14 serves to accommodate a drive mechanism having a piston rod to become operably engaged with a piston of a cartridge to be disposed and fixed in the cartridge holder 12. By way of the inspection window 24, the fluid or filling level of the cartridge can be visually inspected.
The known device 10 as illustrated in FIGS. 1 to 3 is of disposable type. Cartridge holder 12 and body 14 are adapted to be interconnected in a non-releasable way. For this purpose, the insert portion 26 of the cartridge holder 12 comprises several circumferentially distributed through openings 28 of substantially rectangular shape. Correspondingly and as illustrated in FIG. 3, the receiving side wall portion 32 of the body 14 comprises radially inwardly protruding pegs or prongs 34 adapted to mate with the through openings 28 of the cartridge holder as soon as the cartridge holder 12 is appropriately inserted into the body 14 with its insert portion 26.
Radially inwardly protruding prongs 34 further comprise a beveled surface 36 towards their distal end in order to facilitate mutual engagement of prongs 34 and through openings 28. Furthermore, the insert portion 26 of the cartridge holder 12 is delimited in distal direction by a circumferential and radially outwardly extending rim 30, which in a final assembly configuration abuts against a distally located end face 38 of the body 14.
The housing components 12, 14 are typically manufactured as injection moulded plastic components, which, by virtue of appropriately selected thermoplastic materials feature a sufficient elasticity in order to support the snapping in and a resulting positive interconnection of cartridge holder 12 and body 14.
However, since such drug delivery devices 10 are predominately intended for home medication, the device has to fulfill highest possible standards in terms of failure safety and robustness, especially in view of mechanical impact.
If for instance the device 10 drops down from a considerably height, a mechanical load-distribution may rise above a critical level in the interconnection of cartridge holder 12 and body 14. Point stresses or point loading acting on the through opening 28 and/or on the prongs 34 may exceed a critical level and the interconnection of cartridge holder 12 and body 14 may break down, the housing components 12, 14 may release and the device 1 would be no longer of use.
It is therefore an object of the present invention to provide a drug delivery device comprising a robust, reliable and mechanically resistant interconnection of cartridge holder and body. The interconnection should be easily integrable in existing housing designs of drug delivery devices. It should also be easily implementable, both, in terms of production costs and assembly work. Moreover, the interconnection of body and cartridge holder should be intuitive and easy to establish.